Device for deflecting optical beams

ABSTRACT

The invention relates to a device for the deflection of optical beams ( 25 ), provided with a piezo-plate ( 14 ), which has piezoelectric regions ( 15, 16 ), controlled by piezo electrodes ( 20, 21 ). At least one end section ( 22 ) of the piezo plate ( 14 ) is free of piezo electrodes ( 20, 31 ), whereby said free end section ( 22 ) is of a size, corresponding to the dimensions of the beams falling thereon. A deflection is thus achieved which leaves the wavefronts of the beams ( 25 ) essentially undisturbed.

[0001] The invention concerns a device for deflecting optical beams,comprising a piezo plate having piezoelectric regions and comprisingpiezo electrodes, disposed on surfaces, to drive said piezo plate.

[0002] A device of this kind is known from the article “Piezoelectricbimorph optical beam scanners: analysis and construction,” by J. KellyLee, published in Applied Optics, Vol. 18, No. 4, pp. 454-459. In thisprior device, a mirror is mounted on a piezo plate. When the device isdriven by piezo electrodes with a control voltage in the medium voltagerange, the mirror moves as a result of the flexure induced in the piezoplate. A disadvantage of this device is the comparatively high mass thatmust be moved, which is an obstacle to rapid drive.

[0003] The object of the invention is to provide a device of thefirst-cited type that is distinguished by rapid drivability anddistortion-free deflection.

[0004] This object is achieved according to the invention in a device ofthe first-cited type by the fact that the piezo plate is free of piezoelectrodes in at least an end portion.

[0005] Because there are no piezo electrodes in an end portion of thepiezo plate, no flexure is induced in that end portion, which insteadremains substantially planar. If the electrode-free end portion isdimensioned to be relatively large compared to the dimensions of thebeams incident thereon, reflection or transmission by the end portionwill result in little or no distortion of the wave fronts and thus ofthe beam characteristic, especially the divergence.

[0006] Preferred embodiments will become apparent from the dependentclaims.

[0007] Further suitable embodiments and advantages of the invention arethe subject matter of the following description of preferred exemplaryembodiments, provided with reference to the figures in the drawing,wherein:

[0008] FIG. 1 is a perspective view of a first exemplary embodiment ofthe invention, comprising a piezo plate having two piezo layers in whichthe spontaneous polarization has the same orientation,

[0009] FIG. 2 is a perspective view of a second exemplary embodiment ofthe invention, comprising a piezo plate having two piezo layers in whichthe spontaneous polarization is of opposite orientation,

[0010] FIG. 3 is a side view of the second exemplary embodiment of FIG.2 during the deflection of a light beam,

[0011] FIG. 4 is a perspective view of a third exemplary embodiment ofthe invention, comprising capacitive electrodes,

[0012] FIG. 5 is a perspective view of a fourth exemplary embodiment ofthe invention, comprising an internal beam guiding arrangement,

[0013] FIG. 6 is a side view of a fifth exemplary embodiment of theinvention, comprising a piezo plate having two arms for mountingpurposes,

[0014] FIG. 7 is a plan view of the fifth exemplary embodiment shown inFIG. 7,

[0015] FIG. 8 is a perspective view of a sixth exemplary embodiment fortwo-dimensional deflection, and

[0016] FIG. 9 is a side view of a seventh exemplary embodiment of theinvention, comprising regions of alternating orientation.

[0017] FIG. 1 is a perspective view of a first exemplary embodiment ofthe invention. The exemplary embodiment of FIG. 1 comprises a flat piezoplate 1 that has a rectangular base surface and contains two individualpiezo layers 2, 3 in which the spontaneous polarization has the sameorientation, perpendicular to the plane of said piezo layers 2, 3. At afirst narrow end side, piezo plate 1 is clamped into a mounting unit 4by means of two mounting bars 5, 6.

[0018] Each piezo layer 2, 3 is provided on its outward-facing largeside with an outer electrode 7, 8 as a piezo electrode. A middleelectrode 9 is also provided as a piezo electrode between piezo layers2, 3. Each outer electrode 7, 8 and middle electrode 9 extend from thefirst narrow end side toward the opposite, second narrow end side, anend portion 10 of the second narrow end side being free of outerelectrodes 7, 8 and middle electrode 9.

[0019] Each outer electrode 7, 8 is connected electrically to anassigned outer-electrode contact 11, 12, while middle electrode 9 isconnected electrically to a middle-electrode contact 13. The applicationof a voltage in the medium voltage range between middle-electrodecontact 13 and each outer-electrode contact 11, 12, using voltages ofopposite polarity, drives piezo plate 1 to flex longitudinally about thetransverse axis in the region of outer electrodes 7, 8 and middleelectrode 9 and middle electrode 9.

[0020] FIG. 2 is a perspective view of a second exemplary embodiment ofthe invention. In the following explanation, data subscripted “1” referto the crystal coordinate system and data subscripted “2” refer to thecoordinate system of the piezo plate. The exemplary embodiment of FIG. 2includes a flat, crystalline, Y₂-cut piezo plate 14 having a rectangularbase surface and comprising two piezo layers 15, 16, the spontaneouspolarization in the plane of piezo layers 15, 16 being oriented inopposite directions. Piezo layers 15, 16 are, for example, fabricated byheating to effect local domain inversion. The Z₂ axes of the Cartesiancoordinate system of the piezo crystal are oriented parallel to the longside of the piezo plate 14, while the Y₂ axis of the piezo plate 14 isrotated with respect to the Y₁ crystal axis by an angle of typicallyabout 120° to 160°, with the coincident X₁ and X₂ axes as the axis ofrotation. As in the first exemplary embodiment, described with referenceto FIG. 1, the piezo plate 14 is clamped by a first narrow end side intoa mounting unit 17 by means of two mounting bars 18, 19.

[0021] Each piezo layer 15, 16 of piezo plate 14 according to the secondexemplary embodiment is occupied on its outward-facing large side by anouter electrode 20, 21 as a piezo electrode. Each outer electrode 20, 21extends from the first narrow end side toward the opposite, secondnarrow end side, an end portion 22 of the second narrow end sideremaining free of outer electrodes 20, 21.

[0022] Each outer electrode 20, 21 is connected electrically to anassigned outer-electrode contact 23′, 24. The application of a voltagein the medium voltage range between outer-electrode contacts 23, 24drives piezo plate 14 to flex longitudinally about the transverse axisin the region of outer electrodes 20, 21.

[0023] FIG. 3 is a side view of the second exemplary embodimentaccording to FIG. 2 during the deflection of a light beam 25 incident,with a planar wavefront, for example, on end portion 22 free of outerelectrodes 20, 21. When a voltage is applied between outer-electrodecontacts 23, 24, piezo plate 14 flexes only in the region of outerelectrodes 20, 21, while end portion 22 struck by light beam 25 remainsplanar except in a comparatively narrow region of transition to theouter electrodes 20, 21. This results in a reflection behavior similarto that of a plane mirror, and the reflected wavefront is not deformedwith respect to the incident wavefront.

[0024] Similar flexural behavior is demonstrated by the piezo plate 1 ofthe first exemplary embodiment, depicted in FIG. 1.

[0025] FIG. 4 is a perspective view of a third exemplary embodiment ofthe invention, which is presented as an improvement of the secondexemplary embodiment described with reference to FIGS. 2 and 3. It isunderstood that the improving features can also be provided inconnection with the first exemplary embodiment, described with referenceto FIG. 1. In the third exemplary embodiment, depicted in FIG. 4, aplate-like first counterelectrode 26, an elongated second electrode 27,and an elongated supplementary electrode 28 are provided. Firstcounterelectrode 26 is arranged to confront an outer electrode 20, 21.Supplementary electrode 28 is disposed on an outer face of a piezo layer15, 16, for example roughly in the center of end portion 22, and extendstransversely with respect to piezo plate 14. Second counterelectrode 27confronts supplementary electrode 28. The mutually confronting outerelectrodes 20, 21 and first counterelectrode 26 and the mutuallyconfronting supplementary electrode 28 and second counterelectrode 27form capacitively functioning electrodes.

[0026] Counterelectrodes 26, 27 are connected electrically to a firstcounterelectrode contact 29 and a second counterelectrode contact 30,respectively. Supplementary electrode 28 is connected electrically to asupplementary-electrode contact 31, while, in addition, outer electrode21 confronting first counterelectrode 26 is connected to anouter-electrode supplementary contact 32.

[0027] The application of a voltage, typically in the medium voltagerange, to first counterelectrode contact 29 and outer-electrodesupplementary contact 32 and to second counterelectrode contact 30 andsupplementary-electrode contact 31 causes forces to be exerted on piezoplate 14, as a function of the polarity of the applied voltage, betweenthe associated outer electrode 21 and first counterelectrode 26 andbetween supplementary electrode 28 and second counterelectrode 27; theseforces are superimposed on the piezoelectrically exerted forces and,especially if the polarity is appropriate, amplify the deflection.

[0028] In modifications of the third exemplary embodiment described withreference to FIG. 4, only one pair is provided out of confronting outerelectrodes 21 and first counterelectrode 26 and confrontingsupplementary electrode 28 and second counterelectrode 27.

[0029] FIG. 5 is a perspective view of a fourth exemplary embodiment ofthe invention, which includes some of the features of the thirdexemplary embodiment described with reference to FIG. 4; these featureshave been given the same reference numerals and will not be described inmore detail below.

[0030] The fourth exemplary embodiment of FIG. 5 includes highlyreflective outer electrodes 20, 21. A decoupling antireflection coating33 has been deposited in end portion 22 free of outer electrodes 20, 21.In addition, the piezo plate 14 projects by an incoupling portion 34beyond mounting unit 17. Incoupling portion 34 is provided with anincoupling antireflection coating 35 and a reflection coating 36, bymeans of which a light beam 25 can be coupled into piezo plate 14. Aftermultiple reflections on outer electrodes 20, 21, light beam 25 exitspiezo plate 14 without deformation through decoupling antireflectioncoating 33 in end portion 22 free of outer electrodes 20, 21. The exitdirection depends on the electrical drive and the associated flexure ofthe piezo plate 14 longitudinally about the transverse axis.

[0031] FIGS. 6 and 7 are a lateral and a plan view, respectively, of afifth exemplary embodiment of the invention, comprising a piezo plate 37that has the same piezoelectric structure as piezo plate 14 describedwith reference to FIG. 2, taking the form of two piezo layers 38, 39with the spontaneous polarization in the plane of said piezo layers 38,39 oriented in opposite directions. Piezo plate 37 is realized with twooutwardly projecting arms 40, 41 in its middle region. The arms 40, 41are engaged with a tilt mounting 42 by means of which piezo plate 37 isswivelably mounted.

[0032] As in the previously described exemplary embodiments, disposed onthe one side of piezo plate 37 as piezo electrodes are outer electrodes43, 44, which extend from tilt mounting 42 into an end region 45 free ofouter electrodes 43, 44, to permit the reflection of a beam 46 withoutdeformation and with the ability to control the direction of reflection.

[0033] Arranged to confront each other in the end portion on the otherside of piezo plate 37 are a supplementary electrode 47 and acounterelectrode 48, to which, as capacitively functioning electrodes,an electrical voltage in the medium voltage range can be applied.

[0034] The driving of outer electrodes 43, 44, supplementary electrode47 and counterelectrode 48, causes piezo plate 37 to flex longitudinallyabout the transverse axis and to tilt about arms 40, 41.

[0035] FIG. 8 is a perspective view of a sixth exemplary embodiment fortwo-dimensional deflection of a beam, comprising a flat, crystallinepiezo plate 49 with a rotated Y₂ cut and a rectangular base surface,comprising two piezo layers 50, 51. The Z₂ axis of the cartesiancoordinate system of the piezo crystal is oriented at an angle ofapproximately 40° to approximately 60° with respect to the long side ofpiezo plate 49. The spontaneous polarizations of piezo layers 50, 51 areof opposite directions in the piezo-plate 49 of the sixth exemplaryembodiment, and are produced, for example, by heating to effect localdomain inversion. The piezo plate 49 is clamped by a first narrow endside in a mounting unit 52 comprising two mounting bars 53, 54.

[0036] Each piezo layer 50, 51 of the piezo plate 49 according to thesixth exemplary embodiment is occupied on its outward-facing large sideby an outer electrode 55, 56 as a piezo electrode. Each outer electrode55, 56 extends from the first narrow end side toward the opposite,second narrow end side, an end portion 57 of the second narrow end sideremaining free of outer electrodes 55, 56.

[0037] Each outer electrode 55, 56 is connected electrically to anassigned outer-electrode contact 58, 59. The application of a voltage inthe high-voltage range between outer-electrode contacts 58, 59 drivespiezo plate 49 to twist about the longitudinal axis in the transversedirection in the region of outer electrodes 55, 56, so that the endportion 57 can be tilted parallel to mounting unit 52 and a beamincident on end portion 57 can be deflected in a given direction.

[0038] In addition, mounted on a large side of end portion 57 is asupplementary electrode 60, which with a counterelectrode 61 spacedlyconfronting it forms a capacitively functioning electrode pair.Supplementary electrode 60 is connected electrically tosupplementary-electrode contact 62, while counterelectrode 61 isconnected to a counterelectrode contact 63. When supplementary electrode60 and counterelectrode 61 are driven by means of a voltage in thelow-voltage range, piezo plate 49 is flexed longitudinally about thetransverse axis. When the flexure that can be generated by supplementaryelectrode 60 and counterelectrode 61 is superimposed on the tilt thatcan be induced by means of outer electrodes 55, 56, the result istwo-dimensional deflection of a beam incident on end portion 57.

[0039] In an exemplary embodiment not shown, to achieve two-dimensionaldeflection, two devices according to the invention, for exampleaccording to one of the exemplary embodiments of FIGS. 1 to 7, arearranged with respect to each other so that the directions of flexurecan be oriented perpendicular to each other.

[0040] FIG. 9 is a side view of a seventh exemplary embodiment of theinvention. The seventh exemplary embodiment depicted in FIG. 9 comprisesa piezo plate 65 fabricated from a Z₁-cut crystal. The piezo plate 65 isrealized with a number of strip-like first domains 66 and second domains67 extending over the entire thickness as regions of orientation, theorientation of the piezoelectrically operative axes being the same ineach case. In the piezo plate 65, the Y₁ axes of the domains 66, 67 areoriented parallel to the long side, whereas by domain inversion the Z₁axes of the first domains 66 have been oriented oppositely to the Z₁axes of the second domains 67. The Y₁ axes of domains 66, 67 aretherefore also oriented oppositely to each other.

[0041] The piezo plate 65 is clamped at a first narrow end side in amounting unit 68 comprising two mounting bars 69, 70.

[0042] Provided as piezo electrodes along the edge regions of a numberof domains 66, 67, on both large sides of piezo plate 65, are strip-likestrip electrodes 71, 72 that are narrow in comparison to the width ofthe domains 66, 67, with an end portion 73 remaining free of stripelectrodes 71, 72. Voltages of alternating polarity in themedium-voltage range can be applied to a large side of each of theadjacently arranged strip electrodes 71, 72, and mutually confrontingstrip electrodes 71, 72 on different large sides can also be subjectedto voltages of alternating polarity. This causes piezo plate 65 to flexlongitudinally about the transverse axis in the region of stripelectrodes 71, 72 according to the magnitude of the applied voltages,while the end portion 73 free of strip electrodes 71, 72 remainssubstantially planar.

1. A device for deflecting optical beams (25, 46), comprising a piezoplate (1; 14; 37; 49; 65) having piezoelectric regions (2, 3; 15, 16;38, 39; 50, 51; 66, 67) and comprising piezo electrodes (7, 8, 9; 20,21; 43, 44; 55, 56; 71, 72) disposed on surfaces of said regions (2, 3;15, 16; 38, 39; 50, 51; 66, 67) and operating to drive said piezo plate(1; 14; 37; 49; 65), characterized in that said piezo plate (1; 14; 37;49; 65) is free of piezo electrodes (7, 8, 9; 20, 21; 43, 44; 55, 56;71, 72) in at least an end portion (10; 22; 57; 73).
 2. The device asrecited in claim 1, characterized in that said piezo plate (65)comprises, as piezoelectric regions, parallel bands of regions oforientation (66, 67) that extend over the thickness of said piezo plate(65) and in which the spontaneous polarization of adjacent regions oforientation (66, 67) is oppositely oriented in pairs, and in that saidpiezo electrodes are realized as strip-like electrodes (71, 72)extending on the edge sides of said regions of orientation (66, 67). 3.The device as recited in claim 1, characterized in that said piezo plate(1; 14; 37; 49) comprises as piezoelectric regions two piezo layers (2,3; 15, 16; 38, 39; 50, 51), each of which is occupied on its outer largeside by a plate-like piezo electrode (7, 8, 9; 20, 21; 43, 44; 55, 56).4. The device as recited in claim 3, characterized in that said piezolayers (2, 3) exhibit uniformly oriented spontaneous polarizationperpendicular to the plane of said piezo layers (2, 3) and in that amiddle plate-like piezo electrode (9) is disposed between said piezolayers (2, 3).
 5. The device as recited in claim 3, characterized inthat said piezo layers (15, 16; 38, 39; 50, 51) exhibit oppositelyoriented spontaneous polarization in the plane of the piezo layer (15,16; 38, 39; 50, 51).
 6. The device as recited in any of claims 1 to 5,characterized in that a highly reflective coating is deposited on saidend portion (10; 22; 57; 73) free of piezo electrodes (7, 8, 9; 20, 21;43, 44; 55, 56; 71, 72).
 7. The device as recited in claim 5,characterized in that an incoupling portion (34) is free of piezoelectrodes (20, 21) and in that the middle portion extending betweensaid end portion (22) and said incoupling portion (34) is provided witha highly reflective coating.
 8. The device as recited in any of claims 1to 7, characterized in that electrodes (26, 27, 28; 47, 48) thatinteract capacitively with said piezo plate (1; 14; 37; 49; 65) areprovided.
 9. The device as recited in claim 8, characterized in thatarms (40, 41) are disposed on said piezo plate (37) in said middleregion, and in that said piezo electrodes (43, 44) are disposed on theone side of said arms (40, 41) and electrodes (47, 48) that interactcapacitively with said piezo plate (37) are disposed at least on theother side of said arms (40, 41).